[ltp] T42p + Battery Rundown and results

[Henrique de Moraes Holschuh]

On Sat, 16 Feb 2008, David A. Desrosiers wrote:
> design capacity:         71280 mWh
> last full capacity:      25450 mWh

Bad...

> I've been charging these to full, then booting to the Battery Rundown
> utility to run the last bit of power out of them, then charging to full
> again. Lather, rinse, repeat. I've been doing this over the last 2 days
> with both of my 9-cell batteries. 

There are *two* processes that apply to LiION cells: gauge reset, and
cell refresh.

Gauge reset is just to adjust the internal charge meters, i.e. your
battery will read 0% when it is near 0%, not while it has still 15% charge
left :)

To reset the gauge:  Charge to full.  Drain to empty.  Charge to full again.
Do it at a temperature of 25C or thereabouts.   Deep discharges shorten
LiION battery life if you do it too often, so don't do this more than once
every 20 cycles or so.  You don't need any windows utility to do this, the
battery eletronics themselves take care of it, and tp-smapi can be used to
force which battery to discharge, if you need to do that.

Li-ION cell refresh is a lot more difficult, and AFAIK the best you can do
without special hardware and fire hazard safety is to let it charge to full,
then discharge it *very slowly* to zero (e.g. leave the thinkpad sleeping
until it depletes the battery), then charge again to full (to also reset the
gague while at it).  Do it at 20C-25C.

If your batteries are more than 2 years old, and you have NOT kept them most
of this time stored at about 40% charge @ 10C, they're just old.  Don't mess
too much with them, you'll just damage them further.  Do a gauge reset every
20 cycles or so, and start saving $$$ to get a new pack :p

> Or, is there some other way to resuscitate these batteries back into
> some level of usability?  

Other than replacing the cells, which you are better off NOT doing in the
first place?  AFAIK all you can do is to get a new battery pack.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh